FunnyDuck Is there a downside to using PWAs in place of native apps?
Mostly it depends on how much effort a company puts in to their PWAs vs how much effort they put in to their native app. In my experience, there's less functionality and the PWA is a little slower because native apps can be more powerful.
FunnyDuck Also Vanadium has permission for Sensors, does that mean PWAs will also have Sensors permission?
Sensors used to be granted by default. You should be able to remove that permission without any issue. If a PWA wants access to something sensitive it should ask. Like location permission would be PWA asks Vanadium for location permission, then Vanadium will ask you for location permission.
FunnyDuck Is there a way to check / take away permissions?
If you want to see what a website's permissions are, open the site in the regular Vanadium browser, tap the lock to the left of the address, tap permissions. A website isn't automatically allowed to access anything Vanadium has access to and each website is sandboxed and has its own unique permissions.
I don't know the answers to your other questions.